The objective of the primate core is to provide the facility, materials and comprehensive clinical support necessary for the in vivo non-human primate studies of the CFAR investigators. This primate core provides up to 200 macaques, either rhesus or cynomolgus macaques. Virus studies using SIVmac251, SIVmac239, SIVs with deleted genes, pathogenic and non- pathogenic SHIV hybrid viruses are all too well with the expertise of the core. The Core leader, Preston A. Marx and Mr. Agegnehu Gettie, the core manager, have a decade of experience in using and developing primate retrovirus models. Dr. Marx has about 100 publications in simian models covering pathogenesis, vaccines and other topics. The studies to be carried out by the core include: 1. In vivo lymphocyte turnover, virus clearance and in vivo expression of HIV/SIV-co-receptors-David Ho group. 2. In vivo effects of passively administered neutralizing antibody and Mab on viral steady states, pathogenesis and prophylaxis-John Moore group. 3. Labeling to study the turnover of macrophages in infected and uninfected monkeys in vivo-Rhonda Kost group. 4. In vivo quasi-species and drug-resistance-Eric Delwart group. 5. Correlates of protection by SIV delta nef-Ruth Connor group and David Ho group. 6. Mucosal infection by macrophage tropic and T cell tropic SHIV-Cecelia Cheng-Mayer group. 7. Lipid-stabilized SIV antigen presentations-Leo Stamatatos group. 8. Study of species-specific viral tropism that map to regions of the viral genome outside of env-Jeremy Luban group. 9. Dendritic cell infections in vivo-Ralph Steinman and Melissa Pope groups.